Adaptive envelope tracking based on detected transmit signal bandwidth

Abstract

Apparatus and methods for power amplifier envelope tracking systems with automatic control of a slew rate and a mode of an error amplifier of the envelope tracking system. The envelope tracker can include a signal bandwidth detection circuit that processes the envelope signal to generate a detected bandwidth signal, and a control circuit that controls the slew rate of the error amplifier based on the detected signal bandwidth.

What is claimed is: 
     
         1 . An envelope tracker for a power amplifier, the envelope tracker comprising:
 an input configured to receive an envelope signal corresponding to an envelope of a radio frequency signal;   an error amplifier configured to generate a power amplifier supply voltage, the error amplifier including a biasing stage configured to adjust a slew rate of the error amplifier; and   a control circuit configured to adjust the biasing stage based on a bandwidth of the envelope signal.   
     
     
         2 . The envelope tracker of  claim 1  wherein the error amplifier further includes an amplifying stage, and the biasing stage is configured to control a bias of the amplifying stage. 
     
     
         3 . The envelope tracker of  claim 1  wherein the biasing stage includes a plurality of biasing stages, and the control circuit is configured to selectively activate one or more of the plurality of biasing stages to adjust the bias current. 
     
     
         4 . The envelope tracker of  claim 3  further comprising one or more slew rate switches usable to selectively activate the one or more of the plurality of biasing stages. 
     
     
         5 . The envelope tracker of  claim 1  further comprising a bandwidth detection circuit configured to generate a detected bandwidth signal indicating the bandwidth of the envelope signal and to provide the bandwidth signal to the control circuit. 
     
     
         6 . The envelope tracker of  claim 5  wherein the control circuit is configured to process the detected bandwidth signal to determine a number of resource blocks used by the radio frequency signal. 
     
     
         7 . The envelope tracker of  claim 1  wherein the envelope tracker further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when the bandwidth of the envelope signal satisfies a condition. 
     
     
         8 . A radio frequency front end module comprising:
 a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage;   an envelope tracker including an error amplifier configured to generate the power amplifier supply voltage, the error amplifier including a plurality of biasing stages, one or more of the plurality of biasing stages configured to be selectively controlled to adjust a slew rate of the error amplifier, the envelope tracker further including a control circuit configured to selectively activate the one or more of the plurality of biasing stages.   
     
     
         9 . The front end module of  claim 8  wherein the error amplifier further includes an amplifying stage, and the plurality of biasing stages are configured to control a bias of the amplifying stage. 
     
     
         10 . The front end module of  claim 8  further comprising one or more slew rate switches usable to selectively activate the one or more of the plurality of biasing stages. 
     
     
         11 . The front end module of  claim 8  further comprising a bandwidth detection circuit configured to generate a detected bandwidth signal indicating a bandwidth of the envelope signal and to provide the bandwidth signal to the control circuit. 
     
     
         12 . The front end module of  claim 11  wherein the control circuit is configured to process the detected bandwidth signal to determine a number of resource blocks used by the radio frequency signal. 
     
     
         13 . The front end module of  claim 8  wherein the envelope tracker further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when a bandwidth of the envelope signal satisfies a condition. 
     
     
         14 . A mobile device comprising:
 a power amplifier system including a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage, an error amplifier configured to generate the power amplifier supply voltage, and a control circuit, the error amplifier including a plurality of biasing stages configured to bias an amplifying stage, one or more of the plurality of biasing stages configured to adjust a slew rate of the error amplifier, the control circuit configured to control the error amplifier to selectively activate the one or more biasing stages; and   an antenna configured to transmit the amplified radio frequency signal.   
     
     
         15 . The mobile device of  claim 14  wherein the error amplifier further includes an amplifying stage, and the plurality of biasing stages are configured to control a bias of the amplifying stage. 
     
     
         16 . The mobile device of  claim 14  further comprising one or more slew rate switches usable to selectively activate the one or more of the plurality of biasing stages. 
     
     
         17 . The mobile device of  claim 14  further comprising a bandwidth detection circuit configured to generate a detected bandwidth signal indicating a bandwidth of the envelope signal and to provide the bandwidth signal to the control circuit. 
     
     
         18 . The mobile device of  claim 17  wherein the control circuit is configured to process the detected bandwidth signal to determine a number of resource blocks used by the radio frequency signal. 
     
     
         19 . The mobile device of  claim 14  wherein the envelope tracker further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when a bandwidth of the envelope signal satisfies a condition. 
     
     
         20 . The mobile device of  claim 14  further comprising a packaged radio frequency front end module including the power amplifier system.